ucd-aws ignores #!/bin/bash and #cloud-config

[m1keil]

According to the docs:

If the user-data starts with #!, it is assumed that the user-data is a generic shell script, and cloud-init will attempt to execute the data as a script

When testing this:

$ curl http://169.254.169.254/latest/user-data
#!/bin/bash

touch /tmp/USERDATA_WAS_HERE

ucd-aws logs shows:

$ sudo journalctl -b -u ucd-aws
-- Journal begins at Fri 2021-10-22 02:02:16 UTC, ends at Fri 2021-10-22 02:05:50 UTC. --
systemd[1]: Starting micro-config-drive job for AWS...
[3.268514] micro-config-drive version: 45
[3.268635] userdata: Looking for shebang file /var/lib/cloud/aws-user-data
[3.268675] userdata: Shebang found #cloud-config
[3.268682] Parsing user data file /var/lib/cloud/aws-user-data
[3.269054] An error occurred while the yaml file was parsed.
...
systemd[1]: Finished micro-config-drive job for AWS.

The file looks like this:

$ sudo cat /var/lib/cloud/aws-user-data
#cloud-config
users:
  - name: clear
    groups: wheelnopw
ssh_authorized_keys:
  - ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABAQC7VLvf7oKsafgenvyYVnnCHDqakHCtq/SpTzxniaMceh0QPNl8B78qqsJBgspvTNFbVSKLNeUbODQeeC9tgb11q1nvW7ZXZRSY0B957+VmCxGQ681X+YbeYM4RoipGLg1QruzjkLITcARar7tRfUP65WBRo8s5UhyqMwA1cYwLUPNL7OZAUkpOdMVF2wdmjVMGooY9S2JUztFYEnIDsEFeH12yzGkEM9W/d8gEpQDGus+aBgKRoABpqxlCZiEfL7y4Xlcu7YoC6UouqiGPdwz1iocyTH2iTkVio8b/AGVgkoo1WMFo/rGFHAPpuW4RcVcgfOby29BFmap28CYYlqRN msverdlik
#!/bin/bash

touch /tmp/USERDATA_WAS_HERE

It looks like the userdata supplied by the user is appended to some auto-generated userdata (probably by ucd?).

A similar problem occurs with #cloud-init. The entire userdata is appended to the end of /var/lib/cloud/aws-user-data.
So in order to run cloud-init style config, the user actually needs to avoid supplying any first line stanza:

curl http://169.254.169.254/latest/user-data
runcmd:
    - touch /home/clear/hello_world